The invention relates to a mechanical connection between a primary nut and a so-called “failsafe” secondary nut, as well as the assembly thus formed.
The invention is intended in particular for use in the case of a THSA actuator (Trimmable Horizontal Stabilizer Actuator) provided on aircrafts. These actuators comprise two mechanical means, one primary, the other secondary, with the latter being intended to take up the stress when a failure occurs in the primary means. Each of the primary and secondary means is associated with a primary and secondary nut, respectively. In normal operation on the primary means, the forces pass through the primary nut to a ball or roller screw, from a variable tailplane of an aircraft, and vice versa. The secondary nut is mechanically connected to the primary nut in order to follow the latter in its translation movements along the ball or roller screw, without being subjected to any stresses. For this, the secondary nut has a treading complementary to the threading of the ball or roller screw, but having a play therewith, and is connected to the primary nut by means of a radially mounted fusible pin perpendicular to the axis of the screw. The pin, while ensuring that the primary nut is followed by the secondary nut, makes it possible to preserve the play between the threadings of the secondary nut of the screw so that there is no contact between them in normal operation.
In the event of a failure of the primary means, in particular at the level of the primary nut, the forces first pass from the variable tailplane of the aircraft through the primary nut to the secondary nut via the pin. The play between the threadings of the secondary nut and the screw is recovered, causing the transmission of the previous forces from the secondary nut to the screw. However, when the forces that pass are greater than the value of a predetermined load, the pin then acts as a fuse and breaks, thus releasing the secondary nut from the primary nut. Then, the forces pass from the variable tailplane to the screw via the secondary nut, implementing the secondary means of the actuator.
The following disadvantage arises from the fusible pin technology. When assembling the two nuts on the screw, it is necessary to use a complex instrumentation in order to hold the two nuts in a relative position with respect to one another so that the precise play between the threading of the secondary nut and the threading of the screw is present. Thus, the housing of the pin is back-drilled via the two nuts and the pin is put in place. This operation is time-consuming and costly.
An objective of the invention is to propose an assembly formed by the primary nut and the secondary nut, with a simplified and faster assembly, while ensuring optimal reliability in the event of an operation failure of the primary nut. To this end, the invention proposes an assembly comprising a first and a second nut, intended to cooperate with a screw, in particular provided in an adjustable tailplane actuator for an aircraft, and a mechanical connection between the first and the second nut comprising means for fusible driving of the second nut by the first nut, in which the mechanical connection also comprises adjustable spacing means forming a wedge between the first and second nuts. Thus, the use in the mechanical connection of adjustable spacing means forming a wedge between the first and second nuts enables the quick, simple and secure positioning while maintaining the precise play desired, without requiring equipment that is heavy and expensive, both in terms of cost and time, in order to produce the mechanical connection between the two nuts.
Advantageously, but optionally, the assembly comprises at least one of the following features:                the adjustable spacing means are constituted by a wedge capable of being adjusted in thickness;        the adjustable spacing means are constituted by a pealable or separable wedge;        the fusible driving means comprise a fusible link anchored in the first nut and extending into the second nut;        the link is substantially parallel to an axis of the second nut;        the link is screwed into the first nut;        the link comprises a portion with cross-section sized so as to break under a predetermined load;        the link comprises a portion with a cross-section sized so as to break with a predetermined extension.According to the invention, an adjustable tailplane actuator for an aircraft comprising an assembly with at least one of the aforementioned features is also proposed.        